Electric field sensor

ABSTRACT

The invention is a method and means for sensing and measuring an electric field within sea water or any other environmental medium. It contains three pairs of diametrically opposed electric current sensing electrodes that are combined and configured in such manner as to form opposite faces of a cube. Each electrode is segmented to effect a predetermined mosaic pattern; and between each pair thereof, a differential amplifier, having an input impedance that is substantially equal to the operational environmental medium, is connected. A signal-processing system, including a telemetering link, a computer, and/or a readout, is connected to the outputs of the differential amplifiers.

o t United States et [15] 3,641,427

Pittman et al. 1 Feb. 8, 1972 541 ELECTRIC FIELD SENSOR 3,273,311 9/1966Monroe et al. ..340/4 E [72] Inventors: Ed P. Human; Roy A. Sm, both of2,992,325 7/ 1961 Lehan ..325/28 Puma Primary Examiner-Richard A. Farley[73] Assignee: The United Statm of America as Assistant Examiner-H. A.Birmiel represented by the Secretary of the Navy Attorney-Louis A.Miller, Don D. Doty and William T. Skeer [22] Filed: Sept. 24, 1969 [57]ABSTRACT [2 1] Appl' 862642 The invention is a method and means forsensing and measuring an electric field within sea water or any otherenvironmen- [52] US. Cl-

"324/ /4 340/4 R tal medium. It contains three pairs of diametricallyopposed [5 l Int. Cl. .1104!) 13/02 electric current sensing electrodesthat are combined and con- [58] Field of Search ..324/8, 9; 340/4 E figred in such manner as to form, opposite faces of a. cube. Each electrodeis segmented to effect a predetermined mosaic References cued pattern;and between each pair thereof, a differential amplifi- UNITED STATESPATENTS er, hav ng an input impedance that IS substantially equal to theoperational environmental medium, is connected. A slgnal- 3,361,9571/1968 Hings ..324/l processing system, including a telemetering link, acomputer, 3,514,693 5/1970 Cagniard ..324/9 and/or a readout, isconnected to the outputs of the dif- 3,265,972 8/1966 Curry ..340/4 Eferential amplifiers.

15. Claims, 1 l, Drawlng Figures ELECTRIC FIELD SENSOR STATEMENT OFGOVERNMENT INTEREST The invention described herein may be manufacturedand used by or for the Government of the United States of America forGovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION systems usually leave a great deal to bedesired because of the high impedance of the normally small electrodes.Thus, accurate measurements may be obtained only if very little currentis drawn from the electrodes. But to obtain sufficient signal power tooperate amplifiers or meters, it has, in the past, been necessary tospace the electrodes rather far apartperhaps as far apart as tens orhundreds of metersif it is desired to measure weak electrical fields.

Another disadvantage of the prior art systems is that they ordinarilyrequire the potential-measuring array to be accurately laid out, withthe potential sensitive electrodes rigidly mounted at fixed locations,and with the electrical conductors connecting the electrodes secured insuch manner to prevent them from moving with respect to the earthsmagnetic field. Moreover, to obtain measurements of the horizontalmagnetic field components of the earth at the bottom of the sea, theelectrodes and electrical conductors may have to be attached to the seafloor, an operation which is usually quite difficult, since it requiresthe use of divers. And, of course, obtaining electric currentmeasurements at intermediate ocean depths becomes a formidable problem,indeed.

In addition to the above, the measurement of weak vertical electricfield components of the earth in shallow water is frequently impossibleby the prior art sensing techniques, because the required electrodeseparation to do so exceeds the water depth.

The subject invention overcomes most of the disadvantages of the priorart, in that it provides a simple, accurate, and convenient method andmeans for sensing electric currentsand, thus, electrical andelectromagnetic fields-within any accessible environment, including thedeep ocean and shallow water environments of the earth.

SUMMARY OF THE INVENTION The present invention relates generally tomeasuring and testing instruments, and, in particular, it is a methodand means for sensing and measuring the electric currents within anelectric or electromagnetic field. In even greater particularity, theinstant invention is an instrument or system for sensing and measuringthe three orthogonal components of nonuniform electric fields in seawater.

Although as previously suggested, the system'constituting this inventionmay be used in any suitable environmental medium for sensing anyelectric currents or electric fieldssuch as electrostatic andelectromagnetic fieldsbe they of the earth or otherwise, for the purposeof being as brief as possible, the type which is used to sense andmeasure electric fields in water will be described herein, with theunderstanding that the invention is not intended to be limited thereto.Obviously, the making of the transition from one environmental medium toanother would be merely a matter of making design choices to properlydesign the invention therefor, the making of which would be well withinthe purview of one skilled in the art having the benefit of theteachings presented herewith.

It is, therefore, an object of this invention to provide an improvedcurrent-sensing instrument.

Another object of this invention is to provide an improved method andmeans for sensing electric fields within any appropriate environmentalmedium.

Another object of this invention is to provide an improved system forcontinuously sensing, measuring, and indicating the three orthogonaldirection components of nonuniform electric fields in water, sea water,the atmosphere, or any other aqueous or subaqueous medium, as well as inspace or any other medium or location physically feasible.

Still another object of this invention is to provide an improved methodand means for continuously sensing, measuring, and indicating anyanomaly or change occurring within an electric field that is caused byan object foreign thereto passing therethrough or existing therein.

A further objective of this invention is to provide an electric fieldsensing and indicating system which may be read out either at a locationthat is contiguous with the sensor or at a location that is remotetherefrom.

A further object of this invention is to provide an electric current,electric field sensing means that may be mounted on or in, carried by,or connected to, the sea floor, an intermediate water depth in any bodyof water (including the deep and shallow ocean) a buoy, a float, aballoon, a ship, a submarine boat, a tether, an anchor, any carriervehicle, or any suitable combination thereof, as desired for any givenoperational purpose, or as necessary during any given operationalcircumstances.

Another object of this invention is to provide an electric field sensingand indicating means that may be timely placed, disposed, launched(either manually or by suitable machine) from any carrier vehicle orstabilized on stationary platform.

Another object of this invention is to provide a more sensitive andaccurate method and means for constitutes measuring, and reading outelectric currents and fields at locations which would not otherwise beaccessible or at least very difficult to get to.

Another object of this invention is to provide an improved method andmeans for detecting and identifying objects or materials located in seawater or any other environmental medium.

Still another object of this invention is to provide an improvedintrusion sensing and indicating system.

It is also an object of this invention to provide an improved method andmeans for measuring an electric field as substantially a point locationor within such a small area that relatively nonuniform fields may beaccurately measured.

Another object of this invention is to provide an electric current andfield sensing means that is easily and economically manufactured,maintained, and operated.

Other objects and many of the attendant advantages will be readilyappreciated as the subject invention becomes better understood byreference to the following detailed description, when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration ofthe theory of operation of the invention;

FIG. 2 is a schematic diagram of a differential amplifier of the typeincorporated in the invention;

FIG. 3 is pictorial view, with parts broken away, of the cube structureof the invention;

FIG. 4 is a cross-sectional view taken at 44 of FIG. 3;

FIG. 5 is a block diagram of a preferred embodiment of the invention;

FIG. 6 is a block diagram of a system which may incorporate the electricfield sensor portion of the invention to an advantage;

FIG. 7 is another embodiment of a system constituting the subjectinvention;

FIG. 8 depicts still another system arrangement which incorporates theinvention;

FIG. 9 illustrates, in block diagram form, a system for sensing theelectric fields or change in electric fields which occur due to thepresence of passing of, or intrusion of, an ob ject which has an effectthereon;

FIGS. 10 and 10a are quasi-pictorial views of various and sundryapplications to which the subject invention can be put to an advantage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis shown a schematic representation of the invention 21. As may readilybe seen, it is preferably cubic in shape and, thus, contains six sides,respectively designated by reference numerals 22 and 22', 23 and 23',and 24 and 24, with the numeral and numeral primed representing theopposite sides thereof.

For the purpose of briefly disclosing the theory of operation, only theupper and lower sides of the cube, their associated electronics, andtheir interaction with electric currents or fields in the ambientenvironment will be discussed.

The aforesaid sides of cube 21 actually constitute electrodes of specialconstruction, which will be discussed subsequently. Between each pair ofoppositely disposed electrodes is connected a differential amplifier,the input impedance of which should be designed to be substantiallyequal to that of the environmental medium in which the invention isintended to operate. Hence, for example, predesigned differentialamplifier 25 is connected between oppositely disposed electrodes 22 and22'. Amplifier 25 is shown as being located within the cubic structure,and for most practical purposes such location is preferred; however, itshould be understood that it may be located at any suitable place, aslong as the impedance thereof, including that of the electricalconductors thereto and therefrom, is substantially the same as theelectrical impedance of the environmental medium in which the inventionis being used. 7

Once the invention is placed in its field-sensing position,representative vertical currents or electric field components 26 through31 will, for example, travel as shown with respect thereto. Those, suchas 26 and 31, which miss the sensor will continue on their way withoutbeing disturbed; but those, such as 28 through 30, which impact uponelectrode 22 travel toward and along electrical conductor 32 to anappropriate input of differential amplifier 25. After suitableamplification-that is, amplification that is sufficient to make thetotal current flow between electrodes 22 and 22' equal to that whichwould occur had not the subject invention been presentthey continue onthrough electrical conductor 33 to electrode 22 and back into theambient environmental medi- Of course, the other two pairs of electrodesand their respective amplifiers function according to the same principlebut with respect to currents and field components orthogonal thereto.

FIG. 2 depicts a representative circuit which may be used asdifferential amplifier 25, if so desired; however, it should beunderstood that any amplifier that is designed to meet the impedance andamplification requirements may be substituted therefor. Obviously, itwould be well within the purview of one skilled in the art having thebenefit of the teachings presented herewith, to make such selection ordesign such amplifier. In FIG. 2 the opposite walls 35 of the sensorincludes electrodes 36 and 37, with the outputs thereof connected to theinputs of an electrical chopper 38. And the outputs of chopper 38 areconnected through an impedance-matching transformer 39 to an adjustablegain internal amplifier 40 of any appropriate conventional design. Theoutput of amplifier 40 of any appropriate conventional design. Theoutput of amplifier 40 is connected to a demodulator 41 which includes adiode detector 42 and a filter 43 containing a parallel-connectedresistor 44 and capacitor 45 connected between the output of diode 42and ground. The output of demodulator 41 is taken from the cathode ofdiode 42 and is coupled to an output terminal 46.

Because the impedance and amplification characteristics are exceedinglyimportant to the optimum operation of the invention, it is againemphasized that they should be so designed that the current passingtherethrough would not meet any impedance other than that which issubstantially equal to that of the environmental medium in which theinvention is operating. For instance, if electric currents 0r fields arebeing sensed and measured in sea water, the amplification and impedancecharacteristics should be such that the components thereof will passthrough the sensor just as if it were not present, thereby preventingany loss or attenuation thereof due to the sensor taking part in themeasurement thereof.

Referring now to FIG. 3, a preferred structural embodiment 51 of thesensor portion of the invention is shown as having a cubic shaped,electrically nonconductive box or box frame 52 which is preferably onemeter in dimension and to which elec trodes 53 through 58 are mounted onthe sides thereof in such manner that electrodes 53 and 54, 55 and 56,and 57 and 58 form substantially parallel opposite faces thereof. Thegeometrical configuration of frame 52 is, as previously mentioned,preferably a cube with insets or angular cuts as shown. However, itshould be understood that it may be designed to have any configurationthat is necessary to physically fit in any given location or confinementor that will enable it to sense and measure the electric current andfield, regardless of its physical disposition. Each side or electrode iscovered with a mosaic of segments 59 that are made of any suitableelectrode material. Of course, each pair of opposite electrodes has itslow-impedance differential amplifier electrically connectedtherebetween. They may be housed in any appropriate encasement 61,preferably located within the cubic structure per se. Electricalconductors 62 through 67 respectively effect the aforesaid electricalconnections between the electrode pairs and their respective amplifiers,and insulated lead wires 68 are, of course, connected to any desiredutilization apparatus.

Although this particular preferred embodiment of sensor 51-which, ofcourse, is water and/or airtightis shown as being hollow (and thuspossibly filled with air), it should be understood that it may be filledwith oil, plastic, or any suitable substantially incompressible pottingmaterial 69 that will make it strong enough to prevent it fromcollapsing from the ambient pressure to which it might be exposed if itwere located in deep water.

More explicit descriptions of the cube structure is illustrated in FIG.4. Using, as appropriate, tee same reference numerals as were used inconjunction with FIG. 3, frame 52 is shown as having a right-angle cut71 in which a rigid, electrically nonconductive plate 72 is mounted andsecured to frame 52 as by any conventional appropriate electricallynonconductive cement 73. A sheet of copper foil 74 is mounted or bondedon plate 72 in any suitable manner, say, as by any appropriate cement75, and the aforesaid segments 59 are, likewise, mounted on and securedto foil 74, as by any suitable electrically conductive cement 76.Electrode segments 59 may, of course, be made of any appropriateelectrically conductive electrode material-such as, for example, copperor aluminum-and they are electrically interconnected by the aforesaidelectrically conductive cement 76, which also tends to be extendedtherebetween. Cement 76 is used in such manner as will providesufficient bonding strength between foil 74 and each segment; thus, itmay, on occasion, be preferable to allow it to overlap the internalsurface of segments 59, as shown in FIG. 4. On the other hand, if it isdesirable to have the outer surface or face of the mosaic electrode flator relatively smooth, any excess of cement may be removed to make itflush therewith.

The electrode segments, being electrically interconnected, incombination effect the respective electrodes of the invention. They are,likewise, connected through foil 74 to insulated wire 77 which issoldered to foil 74. Because wire 77 extends through a hole 78 innonconductive plate 72, it is held firm therein by a nonconductivecement 79 that effectively completes the insulation thereof while, atthe same time makes a seal, such as a watertight seal, thereat. Ofcourse, the

entire structure of the cubic sensor is such that the inside thereof iscompletely insulated from the outside thereof. Hence, it is waterproofand/or airtight and facilitates the inclusion of the electronicspackageincluding amplifiers, power supplies, batteries, readouts,recorders, telemetering equipment-or any other desired apparatus,equipment, or instrumentation-which, under certain circumstances, wouldbe necessary to make it a self-contained unit.

Referring now to FIG. 5, a generalized teaching of the system comprisingthe invention is presented which includes a cubic electric field sensor81 that contains a trio of orthogonal electric current sensors 82, 83,and 84. First orthogonal electric current sensor 82 contains a wall-Aelectrode 85 and a wall-A electrode 86 which is diametrically opposed towall-A electrode in actual structural configuration. Electrodes 85 and86 are electrically connected to the inputs of a differential amplifier87 that, insofar as it is possible, has an input impedance that issubstantially identical to the impedance of the environmental medium forthe distance between said electrodes. Second orthogonal electric currentsensor 83 contains a wall- B electrode 88 and a wall-B electrode 89which is diametrically opposed to wall-B electrode 88, and both of whichare structurally disposed to make 90 angles, respectively, withelectrodes 85 and 86. Electrodes 88 and 89 are electrically connected tothe inputs of a differential amplifier 91 that also, insofar as it ispossible, has an input impedance that is substantially identical to theimpedance of the environmental medium for the distance betweenelectrodes, like that of differential amplifier 87. Third orthogonalelectric current sensor 84 includes a wall-C electrode 92 and a wall-Celectrode 93 that is diametrically opposed to wall-C electrode 92, andboth of which are structurally disposed to make 90 angles, respectively,with electrodes 85, 86, 88, and 89. Electrodes 92 and 93 areelectrically connected to the inputs of another differential amplifier94 that is similar to amplifiers 87 and 91, in that it, too, insofar asit is possible, has an input impedance that is substantially equal tothe impedance of the environmental medium for the distance betweenelectrodes.

Some environments-such as, for example, in air or in space-have inherentimpedances which are very high and perhaps even approach infinity. Thus,it may not be possible to design differential amplifiers 87, 91, and 94to have an input impedance which is comparable thereto. In suchinstance, they should be designed to have an input impedance which isequal to the conjugate of the complex number of the impedance thereof.So doing, of course, causes the imaginary number portionthereof-representing the inductance or capacitance vector thereofto becancelled out, leaving only the resistance value thereof. When theinvention is intended to be used in water or sea water, this may beeffected within the differential amplifiers themselves, therebyobviating the need for further signal processing for such purpose. Butin air or other environmental mediums, it may be necessary to compensateof the lack of true impedance matching of the input impedance of theamplifiers and the impedance thereof, in order to provide optimumoperation and accuracy. This compensation is performed by a plurality ofmultipliers 105, 106, and 107 respectively connected to the outputs ofamplifiers 87, 91, and 94. Ordinarily, said multipliers should be sodesigned as to multiply by two; however, it should be understood thatthey may be designed to multiply by any given factor that will cause thedesired information to be read out.

The outputs from multiplier 105 through 109 are each connected to therespective inputs of a conventional readout 108 which is constructed andcalibrated in such terms as will enable it to read them out separately,in concert, or in any desired resolution or combination.

FIG. 6 depicts another system in which a sensor 111, similar to thosedisclosed in FIGS. 1 through 5, is incorporated to an advantage, inorder to effect an improved electric, electrostatic, or electromagneticcurrent or field measuring instrument. A lift device 112 is connected byany suitable means to sensor 111 for the support thereof. Likewise ananchor 113 is connected by any suitable means to sensor 111 to help holdit in place. Lift device 112 and anchor 113 vary in construction,depending on the operational medium. Thus, if the operational medium issea water, lift device 112 may be a float having a predeterminedbuoyancy, and anchor 113 may be a weight, hook, or the like. If themedium is air, lift device may, for instance, be a balloon or aircraft,and anchor 113 may be any conventional position controller, weight, orthe like. Obviously, the skilled artisan could easily make the properchoice thereof for any given medium, if he had the benefit of theteachings presented herein.

A cable or other telemetering link 114 which communicates the datasignal from electric field sensor 111 is connected between the outputthereof and the respective inputs of a multiplier 1 15 and a selectorswitch 116. The output of multiplier 115 is connected to another inputof said selector switch, and the output thereof is connected to theinput of any appropriate readout 117 calibrated to indicate and/orrecord the aforesaid data signal in any preferred terms.

FIG. 7, like FIGS. 5 and 6, also shows a particular structure whichincludes the subject invention to an advantage, and in this particularinstance is a system which contains a positioner or support 121 whichmay be of any suitable variety that is called for by the operationalcircumstances or medium. Hence, positioner or support 121 may be aplatform in space, in the atmosphere, on the surface of the sea, or evenunder the sea. As a matter of fact, it may also be mounted on land, aswell. The specific criterion that must be followed, of course, is thatit will support and hold the electric field sensor 122 attached theretofor the purpose of enabling it to sense electric currents and fields atsome predetermined place.

The output of electric field sensor 122 is coupled to the input of atelemetering link 123 and, in this particular instance, is connected tothe input of a radio or sonar transmitter 124 included therein. Theoutput of transmitter 124 is connected to the input of a transmittingtransducer 125 which, obviously, must be designed for the transmissionof either electromagnetic signal energy or acoustical signal energy,depending upon whether transmitter 124 is a radio or sonar system.

Transducer 125 broadcasts its output signal 126 throughout whatevermedium it happens to be located in, and a receiving transducer 127 picksup said signal because it is, likewise, disposed for reception thereofwithin said operational medium.

The output of transducer 127 is connected to a radio or sonar receiver128, the output of which, in this particular case, constitutes theoutput of telemetering link 123. Again, it should be understood thatreceiving transducer 127 should be so designed as to be complementarywith the aforementioned transmitting transducer 125 and should beresponsive to either electromagnetic energy or acoustical energy,depending on whether or not receiver 128 was a radio or a sonarreceiver.

The output from receiver 128, and hence, the output from telemeteringlink 123 is connected to the input of any appropriate readout 129 whichis useful for its intended purposes. Of course, readout 129 may beeither an indicator or a recorder or both, and it may be calibrated inany terms that makes the data signal read out thereby intelligible to ahuman or other operator.

The system of FIG. 8 comprises a very simple disclosure of anotherpreferred method and means for sensing and measuring electric fields.Incorporated therein is an electric field sensor 131 which, for example,may be similar to that disclosed in FIG. 3. The output from electricfield sensor 131 is connected through an appropriate telemetering link132 to the input of a computer 133 for reasons which will be disclosedsubsequently in conjunction with the discussion of the operation of thisparticular system. The output of computer 133 is connected to the inputof a suitable readout 134.

On various and sundry occasions it is desirable and perhaps evennecessary that the subject invention be employed as a method and meansfor detecting and measuring the deviation or change in the earthselectric field within a given area. For this purpose, the system of FIG.9 has been invented, and as may readily be seen therein, it contains anarray of sensors 141 which includes electric field sensors 142 through145. Of course, said array of sensors may be disposed at any suitablelocation on land, on the surface of the sea, on the sea floor, at someintermediate position within the sea, in the atmosphere, or in space, aswarranted by the information desired within any particular one thereof.Hence, it should be understood that the geometrical configuration of theelectric field sensor array is not intended to be limited but may besuch as is necessary during any given operational circumstances. Theoutputs from electric field sensors 142 through 145 are respectivelyconnected to the inputs of a like plurality of transmitters 146 through149, the inputs of which constitute the input of a telemetering link151. The outputs of transmitters 146 through 149 are, likewise,respectively connected to the inputs of a like plurality of transducers152 through 155 which broadcast signals in accordance with theirinherent nature throughout the environmental medium 156 in whichcommunication happens to be the most easily effected. A receivingtransducer 157, adapted for receiving the energy broadcast by theaforesaid transducer 152 through 155, is likewise disposed within medium156. The outputs thereof are connected through a plurality of filters158, 159, 161, and 162 which are respectively tuned in such manner thateach passes only the data signals sensed by the aforementioned electricfield sensors 142 through 1 15. In other words, the aforesaidtransmitters 146 through 149 are tuned at predetermined frequenciesrespectively and, thus, filters 158 through 162 are likewise tuned forthe reception and passing of the respective signals therefrom. Theoutputs of filters 158 through 162 are connected to the inputs of areceiver 163, the output of which constitutes the output of theaforesaid telemetering link 151.

The output of receiver 163 is directly connected to the input of areadout 164, which may be calibrated in any desired terms. Receiver 163,likewise, has its output connected to a computer 165 which may be sodesigned as to perform any mathematical signal processing of the datasignal received thereby to put the intelligence information containedtherein into whatever form would be intelligible to a human or otheroperator. For example, computer 165 may be used as a continuous resolverfor calculating the magnitude and direction of the electric fields beingsensed by sensors 142 through 145 or their respective deviations whichoccur as a result of an intrusion of some foreign object within theearths electric or electromagnetic fields within the area encompassedarray 141. The output of computer 165 is connected to the input of areadout 166, which may be any suitable readout similar to any of theaforementioned readouts.

It would appear to be noteworthy at this particular time that, with theexception of the aforementioned electric field sensors, all of theelements of this invention which have been disclosed herein are wellknown and conventional per se. It is, therefore, to be understood thatit is their unique interconnections and interactions with the aforesaidsensor or sensors and with each other that constitutes the subjectinvention and causes the improved result effected to be producedthereby.

MODE OF OPERATION The operation of the invention will now be discussedbriefly in conjunction with all of the figures of the drawing.

As previously suggested, the potential difference between a pair ofelectrodes disposed within a predetermined environmental medium isproportional to the strength of the electric field within said medium inthe direction of an imaginary line drawn between them. However, in orderto accurately measure said potential difference or the electric currentflowing between the electrodes as a result of said potential difference,it is absolutely necessary that the impedance of the measuringinstrument does not take part in the measurement process. In otherwords, there must be no power loss within the measuring instrumentitself as a result of its effectively acting as a circuit impedance thatis in parallel with impedance of the current path between the electrodesduring the measuring process. But, in order to prevent such action fromoccurring, two things must be done: l the medium within which theelectric current or field is being measured must be removed from betweenthe electrodes, so that no current path exists therein along theimaginary line that is the shortest current path between the electrodes;(2) a current sensor which has an internal impedance that is equal tothat of said environmental medium must be substituted therefor. Hence,when in a fieldsensing position, the sensed current flows into oneelectrode, through the current sensor, and out the opposite electrode,and this occurs as a result of an electric field being present.Moreover, under such circumstances, said current is measured without thefield causing it being changed or modified in a deleterious manner bythe internal impedance of the measuring instrument; therefore, it isindicative of the actual strength thereof.

As shown in FIG. 3, the vectorial components of any electric fieldpresent are measured in three orthogonal directions. Furthermore, thesensor itself is preferably cubic in shape with the linear dimensionspreferably equaling 1 meter.

Electrodes 53 through 58 are constructed with mosaic segments on theoutside in order to improve the signal-tonoise ratio of the entiresensor. The supporting theory for so doing is presented as follows: i

If an electrode surface area is considered to be composed of a largenumber of incremental areas AA, and each AA area is a source of randomnoise, then the total noise current flowing therefrom through thedifferential amplifier is the vector sum of the currents from all AAareas in one electrode minus the vector sum of all the AA currents inthe other coacting electrode. If the AA noise source areas are allstatistically similar and mutually independent, then the vector sum isthe square root of the sum of the squares of the individual sourceareas, and the total noise is proportional to the square root of theelectrode area or the first power of the basic dimension of the cube.The electrode noise power is unaffected by the separation between twoelectrodes, but if the AA noise sources are mutually dependent, then thetotal noise is proportional to the electrode area or the square of thebasic dimension of the cube.

The signal current through the diflerential amplifier due to an electricfield in water, for example, is proportional to the electrode area orthe square of the basic dimension of the cube. The signal voltage acrossthe input terminals of the amplifier is directly proportional to theelectrode separation distance or the first power of the basic dimension.The signal power, which is proportional to the product of the signalvoltage and current, is, therefore proportional to the third power ofthe basic dimension. The signal-to-noise ratio and threshold sensitivityare then proportional to the square of the basic dimension if the AAareas are independent, and they are proportional to the first power ofthe dimension if they are dependent.

But it has been found that the magnitude, distribution, and mutualdependence of the individual noise areas depend upon electrode materialand construction; hence, a considerable degree of mutual independence ofindividual noise sources may be assured by constructing the outersurfaces of the electrodes as mosaics of many individual segments. Thesegments obtained from a single manufacturing batch or run should beevenly distributed between the two electrodes of a coacting pair ofelectrodes, in order to optimize the effects of using such an electrodefabrication technique. In any event, the electrode construction shown inFIGS. 3 and 4, when combined with their associated components, effect aconsiderably improved electric field sensor which ostensively is anadvancement in the art.

A further reduction in signal-to-noise ratio is effected in the subjectdevice because it permits the inclusion of differential amplifiershaving very low input resistancefor example, ap-

proximately one-fourth ohm for a l-meter cube for sea water-and results,therefore, in a much lower level of amplifier noise. It has beendetermined that the amplifier noise is typically reduced by as much as1,000 times or greater. However, for optimum overall operation, thedesign choice of amplifier input impedance is contingent upon theoperational medium within which it is working, and it should besubstantially comparable thereto. Of course, as suggested above, forsensing electric fields in water or sea water, the amplifier inputimpedance would be very low, thereby improving the signalto-noise ratioof the sensor.

A secondary effect contributing to the reduced noise in the invention isthe fact that many of the individual noise sources inherent inelectrodes are of relatively high impedance. When a pair of electrodesis connected through a low-resistance amplifier circuit, the noisesources caused by minute impurities in the electrode materials arerapidly dissipated, and the noise level is substantially less than thatresulting from the same pair of electrodes connected through ahigh-impedance circuit.

In order to detect and measure all of the components of an electricfield, the subject sensor is built with a cubic shape, the area of eachelectrode of which is 1 square meter. Opposing sides of the cubeconstitute the coacting electrodes and, hence, it may readily be seenthat an electric field is, for all practical purposes, sensed at a pointwith respect to three mutually perpendicular directions. Thus, the threevector components of any field are measured and may be appropriatelyresolved into its magnitude and direction by associated apparatus, if sodesired.

In actual practice, the sensor is placed in the environmental mediumwhere the electric field is to be measured. The various and sundryplaces and the means for so doing will be discussed subsequently inconjunction with FIG. 10. Suffice to say at this time that the mediummay be any that is adapted for receiving the cubic sensor. Commonexamples thereof are water, the shallow and deep oceans, atmosphere, andspace, although it is entirely conceivable that it is also possible todispose it in some solids such as ice, plastics, or the like.

The system of FIG. 5 operates in the same manner as that of FIG. 3,inasmuch as the sensors are comparable, even though represented in blockdiagram form therein. However, multipliers 105 through 107 have beenadded thereto for the purpose of compensating for substantially infiniteor at least highimpedance environments in which this system may be usedto an advantage.

The system of FIG. 6 may be used in an environment where it ispreferable to essentially stabilize the position of the electric fieldsensor. Thus, if electric field sensor 111 is to be located at someintermediate depth in the sea, lift device 112 would be designed as asuitable float and anchor 113 would be designed to either hook in thesea floor or hang suspended from sensor 111. Cables or any othersuitable attaching means may be used to connect lift device 112 andanchor 113 to sensor 111. On the other hand, if sensor 111 is to belocated in air, device 112 might be a balloon and anchor 113 anappropriate weight. Obviously, it would be well within the purview ofone skilled in the art having the teaching presented herewith to selectappropriate lift devices and anchors that would operate properly in theintended environmental medi- In the event it is desired that the readoutbe remote from sensor 111, a long insulated electrical cable or othertelemetering link 1 14 is used. Depending on the impedance of theenvironmental medium, multiplier 115 may be included, and so selectorswitch 116 is provided for that purpose. Readout 117, of course, isconventional and may be any type desired.

FIG. 7 shows a system that operates similar to those described above,but it also specifically teaches that the telemetering may be effectedby means of radio or sonar, as any particular operational circumstanceswarrant.

The system of FIG. 8 likewise operates like the aforementioned systems,with the exception that a computer 133 is incorporated therein for thepurpose of resolving the analog signals obtained from electric fieldsensor 131 into intelligible data that represents the field beingmeasured. Obviously, it may be employed to make any other usefulcomputations. Readout 134 is calibrated in terms and with indicia thatwould be significant to a human or other operator.

FIG. 9 depicts a system which may be employed to detect and measure theintrusion of an object within a given area of a predeterminedenvironmental medium, such as water, sea water, air, space, or the like.It operates on the principle that the earth and its ambient environmentcontain or generate electric fields which may be detected and measuredwhich are disturbed by the intrusion or presence of a foreign objecttherein. Hence, if the electric field of the earth is measured at anygiven location and a foreign object intrudes upon said location, theelectric field and its vectoral components are changed in such mannerthat, with proper calibration, the changes thereof will indicate thetype of object involved and the direction of its travel. In order tomake such earth field measurements, however, it is necessary to use aplurality of electric field sensors which are disposed in a suitablearray configuration to monitor the area under consideration or possiblybeing protected. Although the system of FIG. 9 only shows four of suchelectric field sensors, it should be understood that any number thereofmay be similarly employed as the circumstances warrant.

From a practical operational standpoint, once the array of sensors hasbeen located within the particular area of the environmental mediumbeing watched, they each supply electrical signals to respectivetransmitters which, in turn, are connected to a like number oftransmitting transducers for the broadcast thereof throughout theenvironmental medium which would most expeditiously transmit thesignals. Said signals are, of course, received by a receiving transducerthat is compatible with the aforementioned broadcasting transducer, andthe signals thus received thereby are then filtered by a plurality offilters, the based frequency of which is designed to indicate which ofthe aforementioned electric field sensors for sensing an electric fieldhas deviated from its normal condition as a result of the presence of orintrusion of the aforementioned foreign object. The outputs of saidfilters are then supplied to a receiver for suitable signal processingin order to make them more useful as inputs to either a readout directlyor to a computer for suitable computations and readout.

Referring now to FIG. 10, there is illustrated a number of ways in whichthe subject invention may be used to obtain and supply informationregarding the earths electric or electromagnetic fields. For example, anaircraft 171 might be used to tow the subject sensor 172 through theatmosphere 173 to continuously measure the earths electric field as ittravels along. In another situation, a sensor 174 might be submergedfrom a buoy, float, or platform 175 which contains a transmitter 176that is connected to sensor 174 for the purpose of broadcasting theelectric fields sensed thereby in water 177 to some remote receivingstation 178 on land 179. In addition, platform 175 might also have areceiving system 181 suspended therefrom, in order to act as one of thetelemetering or communication relay components of a particulartelemetering link. Still another application of the subject invention isto support a sensor 182 from a balloon 183 with a weight 184 connectedto sensor 182 for the purpose of stabilizing it in space and thusprevent it from swinging unnecessarily. Still another possiblecircumstance which might include the subject invention to an advantagewould be that where a submarine boat I tows a sensor 186 within theoceans 177. In such case, the associated apparatus such as the readoutand the like would probably be disposed within the submarine boat,although it may be located at some other receiving point, if so desired.Still another possible use for the subject invention is to suspend asensor 187 from a float 188 having sufficient buoyancy to hold sensor187 in place within water 177 when it is anchored by a suitable anchoror weight 189 laying on the floor or sea floor 191 thereof. Anothermeans of employing the invention to an advantage would be to tow asensor 192 by means of a cable 193 which is attached to a ship 194. Theassociated apparatus may be, likewise, located within ship 194, or ship194 may include a transmitting means 195 which acts as a relay stationbetween it and the aforementioned remote receiving station 118 which, aspreviously mentioned, could possibly be located on land 179. Of course,when acting as a relay, a receiver 196 located within the water uponwhich ship 194 is traveling would thus cause it to act as acommunication link between remote sonar and radio communicationsstations. Likewise, receiver 197 might also be connected by suitableelectric cables 198 to receiver 178, even through the receiving station197 may be located remote therefrom and possibly be disposed within seawater 177 or the like. As mentioned in conjunction with FIG. 9, an array201 similar thereto may be located on the sea floor, in the 'event it isdesired to determine whether or not the water above it is being intrudedby a submarine, boat, ship, or any other foreign object. Said arraycould include a plurality of sensors 202 through 205 that arerespectively connected to a transmitter 206 which, in turn, is connectedto broadcast transducer 207.

Although each of the foregoing applications of the subject invention areindicated as being suitable to detect and readout the presence offoreign objects that may enter the area, it should be also understoodthat it is possible for them to act as detectors of marine mines 208 and209, in the event that it is possible to measure the earth electricfield at such locations both before and after the placement of saidmines. Under such circumstances, obviously, it would be the deviationfrom the normal electric filed that would alert interested parties tothe fact that certain objects, such as marine mines, had been placednearby.

From the foregoing, it may readily be seen that the subject invention isexceedingly useful because it constitutes an advancement in the electricfield sensing art which makes it more sensitive and accurate for manyoperational purposes.

Obviously, other embodiments and modifications of the subject inventionwill readily come to the mind of one skilled in the art having thebenefit of the teachings presented in the foregoing description and thedrawings. It is, therefore, to be understood that this invention is notto be limited thereto and that said modifications and embodiments areintended to be included within the scope thereof.

What is claimed is:

l. A system for sensing and measuring an electric field within apredetermined environmental medium, comprising in combination:

a first electrode disposed in said predetermined environmental medium insuch manner that only one side thereof is in contact therewith;

a second electrode spatially disposed from said first electrode and,likewise, disposed in predetermined environmental medium in such mannerthat only one side thereof is in contact therewith;

means, having an input impedance substantially equal to the impedance ofsaid environmental medium, connected between the sides of said first andsecond electrodes not in contact with said environmental medium forsensing the current flowing therebetween; and

means connected to the output of said current-sensing means for readingout the current flowing therein.

2. The system of claim 1 wherein said means, having an input impedancesubstantially equal to the impedance of said environmental medium,connected between the sides of said first and second electrodes not incontact with said environmental medium for sensing the current comprisesa differential amplifier.

3. The system of claim 1 wherein said means, having an input impedancesubstantially equal to the impedance of said environmental medium,connected between the sides of said first and second electrodes not incontact with said environmental medium for sensing the currentcomprises:

a chopper;

a transformer having a primary winding and a secondary winding, with theprimary winding thereof connected to the output of said chopper;

a variable gain amplifier connected to the secondary winding of saidtransformer; and

a demodulator connected to the output of said variable gain amplifier.

4. The system of claim 1, wherein said first and second electrodes eachcomprises:

an electrically nonconductive backing plate;

an electrically conductive foil cemented to one side of said backingplate;

a plurality of electrically conductive segments attached to saidelectrically conductive foil in such manner that an electric currentwould readily flow therebetween but in such spatial disposition thatthey are not in physical contact with each other; and

insulated electrical conductor means extending through said electricallynon conductive backing plate and electrically connected at one endthereof to the aforesaid electrically conductive foil.

5. The invention of claim 4 further characterized by means located inthe spaces between said spatially disposed electrically conductivesegments for the holding thereof in a predetermined geometricalconfiguration.

6. The invention of claim 1 further characterized by means effectivelyconnected to said first and second electrodes for the holding of eachthereof in a predetermined position relative to and at a predetermineddistance from the other.

7. The invention of claim 6 wherein said means effectively connected tosaid first and second electrodes for the holding of each thereof in apredetermined position relative to and at a predetermined distance fromthe other comprises a frame having a cubic shape wherein the length,width, and depth dimensions thereof are equal and are substantiallyequal to the length and width dimensions of each of said first andsecond electrodes, with said first and second electrodes mounted in theopposite sides thereof in such manner that the sides of said first andsecond electrodes in contact with the aforesaid environmental mediumface outwardly and in opposite directions.

8. A sensor for sensing an electric field within a predeterminedenvironmental medium, comprising in combination:

a watertight box frame having a cubic shape;

a sextet of electrodes respectively mounted on the six sides of said boxframe in such manner that only one side of each thereof is in contactwith said environmental medium; and

a trio of differential amplifiers, each of which has an input impedancesubstantially equal to that of the aforesaid environmental medium,respectively connected between oppositely disposed electrodes of a trioof pairs of electrodes constituting the aforesaid sextet of electrodes.

9. The system of claim 8 wherein each of said sextet of electrodescomprises:

an electrically nonconductive baking plate;

an electrically conductive foil cemented to one side of said backingplate;

a plurality of electrically conductive segments attached to saidelectrically conductive foil in such manner that an electric currentwould readily fiow therebetween but in such spatial disposition thatthey are not in physical contact with each other; and

insulated electrical conductor means extending through said electricallynonconductive backing plate and electrically connected at one endthereof to the aforesaid electrically conductive foil.

10. The invention of claim 8 further characterized by a readoutconnected to the outputs of the aforesaid trio of differentialamplifiers.

11. The invention of claim 10 further characterized by a telemeteringlink connected between the outputs of said trio of differentialamplifiers and the input of the aforesaid readout.

12. The invention of claim 11 further characterized by a computerconnected between the output of said telemetering link and the input ofthe aforesaid readout.

13. The invention of claim 11 further characterized by:

a selector switch having a pair of inputs and an output, with one of theinputs thereof connected to the output of said telemetering link;

a multiplier connected between the output of said telemetering link andthe other input of said selector switch; and

a readout connected to the output of said selector switch.

14. The invention of claim 8 further characterized by:

a plurality of sensors for sensing an electric field within apredetermined environmental medium, each of which is substantiallyidentical to the aforesaid sensor for sensing

1. A system for sensing and measuring an electric field within apredetermined environmental medium, comprising in combination: a firstelectrode disposed in said predetermined environmental medium in suchmanner that only one side thereof is in contact therewith; a secondelectrode spatially disposed from said first electrode and, likewise,disposed in predetermined environmental medium in such manner that onlyone side thereof is in contact therewith; means, having an inputimpedance substantially equal to the impedance of said environmentalmedium, connected between the sides of said first and second electrodesnot in contact with said environmental medium for sensing the currentflowing therebetween; and means connected to the output of saidcurrent-sensing means for reading out the current flowing therein. 2.The system of claim 1 wherein said means, having an input impedancesubstantially equal to the impedance of said environmental medium,connected between the sides of said first and second electrodes not incontact with said environmental medium for sensing the current comprisesa differential amplifier.
 3. The system of claim 1 wherein said means,having an input impedance substantially equal to the impedance of saidenvironmental medium, connected between the sides of said first andsecond electrodes not in contact with said environmental medium forsensing the current comprises: a chopper; a transformer having a primarywinding and a secondary winding, with the primary winding thereofconnected to the output of said chopper; a variable gain amplifierconnected to the secondary winding of said transformer; and ademodulator connected to the output of said variable gain amplifier. 4.The system of claim 1, wherein said first and second electrodes eachcomprises: an electrically nonconductive backing plate; an electricallyconductive foil cemented to one side of said backing plate; a pluralityof electrically conductive segments attached to said electricallyconductive foil in such manner that an electric current would readilyflow therebetween but in such spatial disposition that they are nOt inphysical contact with each other; and insulated electrical conductormeans extending through said electrically non conductive backing plateand electrically connected at one end thereof to the aforesaidelectrically conductive foil.
 5. The invention of claim 4 furthercharacterized by means located in the spaces between said spatiallydisposed electrically conductive segments for the holding thereof in apredetermined geometrical configuration.
 6. The invention of claim 1further characterized by means effectively connected to said first andsecond electrodes for the holding of each thereof in a predeterminedposition relative to and at a predetermined distance from the other. 7.The invention of claim 6 wherein said means effectively connected tosaid first and second electrodes for the holding of each thereof in apredetermined position relative to and at a predetermined distance fromthe other comprises a frame having a cubic shape wherein the length,width, and depth dimensions thereof are equal and are substantiallyequal to the length and width dimensions of each of said first andsecond electrodes, with said first and second electrodes mounted in theopposite sides thereof in such manner that the sides of said first andsecond electrodes in contact with the aforesaid environmental mediumface outwardly and in opposite directions.
 8. A sensor for sensing anelectric field within a predetermined environmental medium, comprisingin combination: a watertight box frame having a cubic shape; a sextet ofelectrodes respectively mounted on the six sides of said box frame insuch manner that only one side of each thereof is in contact with saidenvironmental medium; and a trio of differential amplifiers, each ofwhich has an input impedance substantially equal to that of theaforesaid environmental medium, respectively connected betweenoppositely disposed electrodes of a trio of pairs of electrodesconstituting the aforesaid sextet of electrodes.
 9. The system of claim8 wherein each of said sextet of electrodes comprises: an electricallynonconductive backing plate; an electrically conductive foil cemented toone side of said backing plate; a plurality of electrically conductivesegments attached to said electrically conductive foil in such mannerthat an electric current would readily flow therebetween but in suchspatial disposition that they are not in physical contact with eachother; and insulated electrical conductor means extending through saidelectrically nonconductive backing plate and electrically connected atone end thereof to the aforesaid electrically conductive foil.
 10. Theinvention of claim 8 further characterized by a readout connected to theoutputs of the aforesaid trio of differential amplifiers.
 11. Theinvention of claim 10 further characterized by a telemetering linkconnected between the outputs of said trio of differential amplifiersand the input of the aforesaid readout.
 12. The invention of claim 11further characterized by a computer connected between the output of saidtelemetering link and the input of the aforesaid readout.
 13. Theinvention of claim 11 further characterized by: a selector switch havinga pair of inputs and an output, with one of the inputs thereof connectedto the output of said telemetering link; a multiplier connected betweenthe output of said telemetering link and the other input of saidselector switch; and a readout connected to the output of said selectorswitch.
 14. The invention of claim 8 further characterized by: aplurality of sensors for sensing an electric field within apredetermined environmental medium, each of which is substantiallyidentical to the aforesaid sensor for sensing an electric field within apredetermined environmental medium, and each of which is spatiallydisposed relative to the others and the aforesaid sensor within saidenvironmental medium in such manner as to form an array thereof havIng apredetermined geometrical configuration; a readout; and a telemeteringlink connected between the outputs of each of said sensors and the inputof the aforesaid readout.
 15. The invention of claim 14 furthercharacterized by a computer connected between the output of saidtelemetering link and the input of said readout.